The present invention provides devices and methods for the endoluminal placement of prostheses, particularly within the vascular system for the treatment of cardiovascular disease, such as vascular stenoses, dissections, aneurysms, and the like. The apparatus and methods, however, are also useful for placement in other body lumens, such as the ureter, urethra, biliary tract, gastrointestinal tract and the like, for the treatment of other conditions which may benefit from the introduction of a reinforcing or protective structure within the body lumen. The prostheses will be placed endoluminally. As used herein, xe2x80x9cendoluminallyxe2x80x9d will mean placement by percutaneous or cutdown procedures, wherein the prosthesis is transluminally advanced through the body lumen from a remote location to a target site in the lumen. In vascular procedures, the prostheses will typically be introduced xe2x80x9cendovascularlyxe2x80x9d using a catheter over a guidewire under fluoroscopic guidance. The catheters and guidewires may be introduced through conventional access sites to the vascular system, such as through the femoral artery, or brachial and subclavian arteries, for access to the target site.
An endoluminal prosthesis typically comprises at least one radially expansible, usually cylindrical, body segment. By xe2x80x9cradially expansible,xe2x80x9d it is meant that the body segment can be converted from a small diameter configuration (used for endoluminal placement) to a radially expanded, usually cylindrical, configuration which is achieved when the prosthesis is implanted at the desired target site. The prosthesis may be non-resilient, e.g., malleable, thus requiring the application of an internal force to expand it at the target site. Typically, the expansive force can be provided by a balloon catheter, such as an angioplasty balloon for vascular procedures. Alternatively, the prosthesis can be self-expanding. Such self-expanding structures are provided by a temperature-sensitive superelastic material, such as Nitinol, which naturally assumes a radially expanded condition once an appropriate temperature has been reached. The appropriate temperature can be, for example, a temperature slightly below normal body temperature; if the appropriate temperature is above normal body temperature, some method of heating the structure must be used. Another type of self-expanding structure uses resilient material, such as a stainless steel or superelastic alloy, and forming the body segment so that it possesses its desired, radially-expanded diameter when it is unconstrained, e.g., released from radially constraining forces a sheath. To remain anchored in the body lumen, the prosthesis will remain partially constrained by the lumen. The self-expanding prosthesis can be delivered in its radially constrained configuration, e.g. by placing the prosthesis within a delivery sheath or tube and retracting the sheath at the target site. Such general aspects of construction and delivery modalities are well-known in the art and do not comprise part of the present invention.
The dimensions of a typical endoluminal prosthesis will depend on its intended use. Typically, the prosthesis will have a length in the range from 0.5 cm to 10 cm, usually being from about 0.8 cm to 5 cm, for vascular applications. The small (radially collapsed) diameter of cylindrical prostheses will usually be in the range from about 1 mm to 10 mm, more usually being in the range from 1.5 mm to 6 mm for vascular applications. The expanded diameter will usually be in the range from about 2 mm to 42 mm, preferably being in the range from about 3 mm to 15 mm for vascular applications.
One type of endoluminal prosthesis includes both a stent component and a graft component. These endoluminal prostheses are often called stent grafts. A stent graft is typically introduced using a catheter with both the stent and graft in contracted, reduced-diameter states. Once at the target site, the stent and graft are expanded. After expansion, the catheter is withdrawn from the vessel leaving the stent graft at the target site.
Grafts are used within the body for various reasons, such as to repair damaged or diseased portions of blood vessels such as may be caused by injury, disease, or an aneurysm. It has been found effective to introduce pores into the walls of the graft to provide ingrowth of tissue onto the walls of the graft. With larger diameter grafts, woven graft material is often used. In small diameter vessels, porous fluoropolymers, such as PTFE, have been found useful.
Coil-type stents can be wound about the catheter shaft in torqued compression for deployment. The coil-type stent can be maintained in this torqued compression condition by securing the ends of the coil-type stent in position on a catheter shaft. The ends are released by, for example, pulling on wires once at the target site. See, for example, U.S. Pat. Nos. 5,372,600 and 5,476,505. Alternatively, the endoluminal prosthesis can be maintained in its reduced-diameter condition by a sleeve; the sleeve can be selectively retracted to release the prosthesis. A third approach is the most common. A balloon is used to expand the prosthesis at the target site. The stent is typically extended past its elastic limit so that it remains in its expanded state after the balloon is deflated. One balloon expandable stent is the PALMAZ-SHATZ stent available from the CORDIS Division of Johnson and Johnson. Stents are also available from Arterial Vascular Engineering of Santa Rosa, Calif. and Guidant Corporation of Indianapolis, Ind.
The present invention is directed to an endoluminal prosthesis configured to help avoid trauma to a patient""s tissue.
One aspect of the invention is directed to a coiled stent having a coiled stent body with a main body portion and end portions. The end portions are substantially less stiff than the body portion to help prevent tissue trauma.
The main body portion may include a ladder-like stent having edge elements separated by connector elements. The end portions may have inwardly-tapering portions with blunt tips. The inwardly-tapering portions may have lengths greater than the widths. The main body portion may also be designed to have longitudinal sections with different radial stiffnesses.
A graft material may be used to cover at least the main body portion to create a coiled stent graft in which adjacent turns have gaps defined therebetween to create a generally helical gap. The generally helical gap helps to promote a helical pattern of tissue ingrowth so that even if substantial tissue ingrowth occurs, the vessel will be much less likely to be sealed off than if the exposed tissue defined a circular pattern. The use of the generally helical gap may help speed up healing because the generally helical gap may help cells to proliferate more evenly between the coils and may enhance non-turbulent flow to help reduce restenosis.
Further aspects of the invention relates to an endoluminal prosthesis having a body with side elements separated by connector elements and a placement method therefore. The body is placeable in a contracted, reduced diameter state and a relaxed, expanded state. The connector elements are generally parallel to the axis of the body when placed in the contracted, reduced-diameter state, typically surrounding a placement catheter.
According to another aspect of the invention the endoluminal prosthesis includes a coiled body having first and second ends and a main portion therebetween. The main portion has an average cross-sectional dimension of x. At least one of the first and second ends has a maximum cross-sectional dimension of about 5 x to 25 x and a blunt tip to avoid trauma to the patient""s tissue. The tip typically has a flattened, generally oval shape while the main body portion typically has a rectangular cross-sectional shape.